1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device which arranges a protective element (diode element) for electrostatic protection in the inside of a display panel.
2. Description of Related Arts
A TFT-type liquid crystal display module which uses thin film transistors as active elements can display a high-definition image and hence, the liquid crystal display module has been used as display devices of television receiver sets, displays of personal computers and the like. Particularly, a miniaturized TFT-type liquid crystal display device has been popularly used as a display part of a mobile phone.
In general, in the liquid crystal display module, in a region surrounded by two neighboring scanning lines (also referred to as gate lines) and two neighboring video lines (also referred to as source lines or drain lines), a thin film transistor which is turned on in response to a scanning signal from the scanning line and a pixel electrode to which the video signal from the video line is transmitted via the above-mentioned thin film transistor are formed thus constituting a so-called pixel.
Conventionally, to prevent electrostatic breakdown attributed to static electricity (for example, breaking of the thin film transistor attributed to static electricity or the like) during manufacturing steps of the liquid crystal display panel, as shown in FIG. 8, a protective circuit (HOGC) is formed on one of substrates which constitute the liquid crystal display panel on an outer portion of the substrate.
Particularly, among thin film transistors, the thin film transistor which uses polysilicon as a material of a semiconductor layer exhibits, compared to a thin film transistor which uses amorphous silicon as a material of a semiconductor layer, high performance as an MOS transistor but a low breakdown voltage and hence, the thin film transistor which uses the polysilicon-made semiconductor layer requires protection against electrostatic breakdown attributed to static electricity. In FIG. 8, symbol VDSC indicates a video voltage selection circuit, symbol VSCA indicates a vertical scanning circuit, symbol TEST indicates an inspection circuit, and symbol SECL indicates a cell cutting line.